The present invention relates in general to Low NO.sub.x Cell.TM. burners in large scale utility boilers, and in particular, to a new and useful cell burner arrangement which utilizes one or more inverted cells, in conjunction with or independently of excess air injected through a lower hopper throat of the boiler furnace or through the side walls of the burner furnace, and further either in conjunction with or independently of shallow angle impellers in the burners of the cells, for significantly reducing CO and H.sub.2 S gaseous concentrations in addition to providing low NO.sub.x characteristics.
Standard cell and Low NO.sub.x Cell burners are known for use in the furnace of boilers, in particular, in utility size boilers. A standard cell burner comprises a pair of closely and vertically spaced coal burners with nozzles and air supplies for producing a dual flame in the furnace wall. In a Low NO.sub.x Cell burner, the upper coal nozzle is replaced by a secondary air port having louvers and other secondary air directing mechanisms for use in conjunction with the lower coal burner nozzle. The lower nozzle is enlarged to accommodate the same fuel input capacity as the two nozzles in the standard design.
It is also known to use one or two rows of Low NO.sub.x Cell burners in the front and rear walls of a utility boiler furnace, with the louvered secondary air port always occupying the upper position in each cell.
One advantage of the Low NO.sub.x Cell design is that it can be retrofit into existing boilers utilizing the standard cell burner architecture.
A number of tests have revealed that while NO.sub.x reductions are enjoyed by the retrofit furnaces, unexpectedly high carbon monoxide (CO) and hydrogen sulfide (H.sub.2 S) concentrations have been found in the ash hopper of the furnace. The high CO concentration may represent a safety and health risk for plant personnel working near the pressure-fired units in the event of a furnace gas leak. The high H.sub.2 S concentrations can increase furnace wall tube corrosion rates.
The construction of a standard Low NO.sub.x Cell burner, including a coal nozzle and a secondary air port, is disclosed in "Comprehensive Report to Congress Clean Coal Technology Program", U.S. Department of Energy, July 1990. Also see, two technical papers by Babcock and Wilcox, entitled "NO.sub.x Control Update-1989", BR-1370, Mar. 5-9, 1989, and "Coal-Fired NO.sub.x Emission Control Technologies", BR-1392, Sep. 25-29, 1989. The retrofitting of Low NO.sub.x Cell burners, to replace standard double burners, is also disclosed in "Development of a Retrofit Low NO.sub.x Burner", M. J. Clark, et al., J. ASME/IEEE Power Generation Conference, Oct. 19-23, 1986.